The present disclosure relates to a fixing device fixing a toner image onto a sheet and an image forming apparatus including the fixing device.
Conventionally, an electrographic image forming apparatus, such as a copying machine or a printer, includes a fixing device fixing a toner image onto a sheet (a recording medium).
For example, there is the fixing device including a fixing belt, a pressuring member coming into pressure contact with the fixing belt to form a fixing nip, a pressing member pressing the fixing belt to a side of the pressuring member and a heat source radiating a radiant heat.
In the fixing device with such a configuration, when the fixing belt is directly heated by the heat source, there are problems that excessive temperature rise of the fixing belt is caused and a property (a heat resisting property) of a lubricant applied between the fixing belt and the pressing member is deteriorated. Further, there are problems that the fixing belt is deformed by the excessive temperature rise of the fixing belt, and then, contact between a contact type temperature detecting part (a thermistor) and the fixing belt is lost to lose general control and a distance between a non-contact type excessive temperature rise preventing device (a thermostat) and the fixing belt is varied.
Thereupon, in the fixing device with the above-mentioned configuration, a heat transmitting member coming into contact with an inner circumference face of the fixing belt is heated by the heat source and the fixing belt is heated by heat transmitted from the heat transmitting member.
However, in the fixing device with the above-mentioned configuration, the heat transmitting member may not come into contact with the fixing belt at a corresponding area to the fixing nip. In such a case, the heat cannot be transmitted from the heat transmitting member to the fixing belt at the corresponding area to the fixing nip and it is feared that it becomes difficult to surely fix the toner image onto the sheet. Moreover, a warm-up time (a time required for heating the fixing nip to temperature allowing the toner image to be fixed onto the sheet) is lengthened and it is feared that energy saving performance is deteriorated.